CN111270155A - Preparation method of spring steel hot-rolled steel strip for safety belt - Google Patents
Preparation method of spring steel hot-rolled steel strip for safety belt Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/10—Supplying or treating molten metal
- B22D11/11—Treating the molten metal
- B22D11/114—Treating the molten metal by using agitating or vibrating means
- B22D11/115—Treating the molten metal by using agitating or vibrating means by using magnetic fields
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/04—Removing impurities by adding a treating agent
- C21C7/06—Deoxidising, e.g. killing
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/10—Handling in a vacuum
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C33/00—Making ferrous alloys
- C22C33/04—Making ferrous alloys by melting
- C22C33/06—Making ferrous alloys by melting using master alloys
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
- B21B2001/225—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length by hot-rolling
Abstract
The invention discloses a preparation method of a spring steel hot rolled steel strip for a safety belt, which comprises the working procedures of electric furnace smelting, LF refining, VD vacuum treatment, continuous casting, heating, rolling, cooling and coiling. According to the invention, a deoxidation furnace protecting agent is added for deoxidation before electric furnace tapping, so that the oxygen content of molten steel is ensured to be within 300ppm during tapping, the inclusion content is reduced, and meanwhile, the initial components of molten steel for LF refining reach 70-90% of the lower limit of the target component range; fine adjustment is carried out on LF refining according to target components; the four-stream special tundish is adopted for casting, so that the purity of the steel billet is improved; by controlling the heating, rolling and coiling temperatures, the decarburized layer on the surface of the hot rolled steel strip is reduced. The finished steel belt product prepared by the invention has fine and uniform structure, good toughness and long fatigue life of the processed coil spring, and has very wide popularization prospect in the fields of automobile safety belts and the like.
Description
Technical Field
The invention relates to a preparation method of a hot rolled spring steel strip for an insurance belt, in particular to a preparation method of a special 62Si2MnA hot rolled spring steel strip for an automobile insurance belt.
Background
The seat and the safety belt are combined together through the fastener, so that the automobile safety belt spring is an indispensable part on an automobile. The raw materials for preparing the automobile safety belt spring comprise spring steel such as 62Si2MnA and the like, and the market of the automobile safety belt spring is obviously expanded along with the development of the automobile industry in China.
The 62Si2MnA spring steel is high-carbon steel, generally adopts an ultrahigh power electric arc furnace for smelting, has fast production rhythm, adopts an eccentric furnace bottom to leave steel and slag and tap steel, and has the defects that the oxygen content of molten steel at the smelting end point is difficult to control, the oxygen content fluctuation is large, the yield of alloy elements is unstable during tapping deoxidation alloying, the fluctuation of components reaching an LF refining furnace is large, the target component control of the LF refining furnace is difficult, the initial oxygen content of molten steel is high, and the inclusion content of the initial molten steel is also high. Meanwhile, most of the existing continuous casting machines adopt five-flow tundish casting blanks, although the surface quality is good, the difference of purity in each flow of casting blanks is large, water model tests show that the tundish is not uniformly distributed smoothly, dead zones exist in two flows at the edge part, the mixing of molten steel components and temperature is not facilitated, and impurities float upwards, wherein the structural schematic diagram of the five-flow tundish is shown in figure 1. In addition, 62Si2MnA spring steel is susceptible to decarburization during billet heating.
Disclosure of Invention
The purpose of the invention is as follows: the invention provides a preparation method of a spring steel hot-rolled steel strip for a safety belt, which can greatly improve the purity and the structure uniformity of the spring steel, has few surface decarburized layers and prolongs the fatigue life of the spring steel for the safety belt.
The technical scheme is as follows: the technical scheme adopted by the invention is a preparation method of a spring steel hot rolled steel strip for a safety belt, which comprises the following working procedures of electric furnace smelting, LF refining, VD vacuum treatment, continuous casting, heating, descaling, rolling, cooling and coiling:
(1) electric furnace smelting: smelting molten steel by using an electric furnace, adding lime and dolomite into the furnace, controlling oxygen supply, adding a deoxidation furnace protecting agent at the smelting end point, and tapping at an eccentric furnace bottom, wherein the content of C in the molten steel is controlled to be more than or equal to 0.10 percent, the content of P is controlled to be less than or equal to 0.010 percent, and the content of oxygen is controlled to be less than or equal to 300ppm during tapping;
(2) LF refining: adding alloy into the furnace to perform molten steel alloying, adding a recarburizing agent to perform diffusion deoxidation, adding lime and fluorite to perform slagging, refining for 40-70 min, keeping white slag for 30-50 min, and controlling Al in the slag2O3The content is less than or equal to 6 percent;
(3) VD vacuum treatment: the vacuum degree is less than or equal to 1mbar, the processing time is more than 10min, and argon is stirred for more than 30min after vacuum breaking;
(4) continuous casting: casting by adopting a four-flow tundish, wherein the superheat degree is 15-35 ℃, and the drawing speed is 1.30-1.40 m/min, so as to prepare a small rectangular blank;
(5) heating: heating the small rectangular blank by adopting a three-section continuous steel pushing type heating furnace, wherein the temperature of a heating section is 1060-1160 ℃, the temperature of a soaking section is 1060-1120 ℃, and the temperature difference of the section of the small rectangular blank is less than 30 ℃;
(6) rolling: descaling the heated small rectangular blank by high-pressure water, and then rolling, wherein the rolling comprises rough rolling, medium finish rolling and final rolling, the rough rolling adopts reciprocating type multi-pass rolling, and the initial rolling temperature is 1030-1110 ℃; the initial rolling temperature of the medium precision rolling is 950-1030 ℃, and the thickness tolerance is controlled; the finishing temperature is 800-870 ℃;
(7) cooling and coiling: and air-cooling and coiling the rolled steel strip, wherein the coiling temperature is less than or equal to 680 ℃.
Preferably, at the end of the smelting step in the step (1), the initial composition of the molten steel is 70 to 90% of the lower limit of the target composition.
Preferably, in the step (2), the LF refining is finely adjusted according to the target composition of the molten steel.
More preferably, the molten steel comprises the following target components in percentage by weight: c: 0.60 to 0.64%, Si: 1.70-1.90%, Mn: 0.70-0.85%, P: less than or equal to 0.015%, S: less than or equal to 0.005 percent, Cr: 0.15 to 0.24%, Ni: less than or equal to 0.10 percent, Cu: less than or equal to 0.12 percent, and the balance of iron and trace elements.
Preferably, the alloy added in the step (2) is low-aluminum low-titanium ferrosilicon and silicon-manganese alloy.
Preferably, the carburant added in step (2) is graphite.
Preferably, the heating atmosphere in the step (5) is a reducing atmosphere, and the residual oxygen content of the flue gas is controlled to be less than or equal to 3 percent.
Preferably, the thickness tolerance of the finish rolling in the step (6) is less than 0.05 mm.
In the electric furnace smelting process, the steel is discharged from the eccentric furnace bottom, so that the slag discharge amount is greatly reduced, the oxidability of the molten steel is greatly reduced, the yield of alloy elements can be improved, the using amount of a carburant is reduced, the production cost is reduced, the content of impurities in the steel can be reduced, and the purity of the molten steel is improved.
The LF refining adopts low aluminum alloy to carry out molten steel alloying, high-purity silicon carbide or high-purity graphite carbon material to carry out deoxidation, lime and fluorite slag systems are adopted to achieve the effect of rapidly removing S from the molten steel, and simultaneously, foam is generated to realize slag submerged arc operation and reduce the N absorption amount of the molten steel.
The continuous casting process adopts small rectangular billet continuous casting, adopts four-flow tundish casting, shortens the molten steel mixing time and increases the residence time by optimizing the flow field of the tundish, and the residence time of the molten steel in each flow is close to each other, so that the effective floating time of impurities is increased, and the purity of the cast steel billet is further improved.
Wherein, the heating procedure adopts low-temperature slow burning and high-temperature fast burning under reducing atmosphere, the residual oxygen content of the flue gas is controlled to be less than or equal to 3 percent, and the decarburization on the surface of the casting blank is reduced.
Has the advantages that: compared with the prior art, the invention has the following remarkable advantages:
(1) the steel strip finished product prepared by the invention has low inclusion content, small chemical component fluctuation and stable performance of different batches of materials;
(2) the surface decarburization of the steel strip finished product prepared by the invention is less;
(3) the finished steel belt product prepared by the invention has fine and uniform structure, good toughness and long fatigue life of the processed coil spring, and has very wide popularization prospect in the fields of automobile safety belts and the like.
Drawings
FIG. 1 is a schematic view of a five-stream tundish configuration used in a continuous caster of the prior art;
FIG. 2 is a schematic view showing the construction of a four-strand tundish used in the continuous casting machine of the present invention.
Detailed Description
The technical solution of the present invention is further described below with reference to the accompanying drawings and examples.
In the examples of the present invention, the percentage content of each chemical composition is a weight percentage content.
Example 1
A preparation method of a 62Si2MnA spring steel hot-rolled steel strip sequentially comprises the following working procedures of electric furnace smelting, LF refining, VD vacuum treatment, continuous casting, heating, descaling, rolling, cooling and coiling, and specifically comprises the following steps:
(1) electric furnace smelting: 40 tons of scrap steel and 70 tons of molten iron are added into an electric furnace, 4000kg of lime and 600kg of dolomite are added in the process of smelting molten steel, and the oxygen supply amount is controlled to be 5000m3290kg of deoxidation furnace protecting agent is added at the smelting end point, the mixture stays for 1min, steel is tapped through an eccentric furnace bottom, and the C content, the P content and the oxygen content in the molten steel are controlled to be 0.15 percent, 0.005 percent and 260ppm respectively during tapping; the initial composition of the molten steel reaches 80% of the lower limit of the target composition.
(2) LF refining: adding 2000Kg of low-aluminum low-titanium ferrosilicon alloy into an LF refining furnace for molten steel alloying, adding 150Kg of high-purity graphite in a small amount and multiple batches for diffusion deoxidation, adding 750Kg of lime and 150Kg of fluorite for slagging, controlling the refining time to be 50min, keeping the white slag for 40min, and controlling the Al2O3 content in the slag to be 6%; the molten steel comprises the following target components in percentage by weight: c: 0.62%, Si: 1.81%, Mn: 0.75%, P: 0.007%, S: 0.002%, Cr: 0.19%, Ni: 0.02%, Cu: 0.04% and the balance of iron and trace elements.
(3) VD vacuum treatment: and after the molten steel components of LF refining are qualified, VD vacuum degassing is carried out, the vacuum degree is 0.5mbar, the processing time is 10min, the covering agent is added after vacuum breaking, argon is blown softly and the stirring is carried out for 60min, and the slag surface is slightly moved and does not see light during static stirring.
(4) Continuous casting: after the molten steel is subjected to VD vacuum treatment, the molten steel is hung and wrapped to a billet continuous casting machine for casting, a four-flow special tundish with a continuous casting nozzle aperture of phi 38mm and a Y-shaped retaining wall is adopted for casting, and as shown in figure 2, a small rectangular billet with the size of 150mm multiplied by 220mm is prepared by casting at the constant casting speed of 1.40m/min at the superheat degree of 21 ℃. Wherein the specific water amount is 0.60L/kg, the electromagnetic stirring frequency of the crystallizer is 3.50Hz, and the current is 350A; the electromagnetic stirring frequency at the tail end is 8Hz, and the current is 300A; the center segregation, the center shrinkage cavity and the center porosity of the casting blank are all lower than 1.0 level. The molten steel of the tundish has long retention time, the retention time of each flow of molten steel is close, the components and the temperature are uniform, the dead zone volume is small, and nonmetallic inclusions can be fully collided, grown and floated to be removed.
(5) Heating: the small rectangular billet with the diameter of 150mm multiplied by 220mm is put into a three-section continuous steel pushing type heating furnace and is heated in a reducing atmosphere, and the residual oxygen content of the flue gas is 2.1 percent. The heating temperature of the heating section of the heating furnace is controlled to be 1120 ℃, the temperature of the soaking section is controlled to be 1070 ℃, and the temperature difference of the section of the billet is less than 30 ℃.
(6) Rolling: and descaling the heated small rectangular billet with the diameter of 150mm multiplied by 220mm by high-pressure water, and then sending the billet into rolling procedures including rough rolling, medium finish rolling and final rolling. Wherein the rough rolling adopts a reciprocating phi 650 and phi 500 rough rolling unit for multi-pass rolling, the initial rolling temperature is 1085 ℃, and the rough rolling is carried out for 6 passes and then the intermediate rolling is carried out; the middle finish rolling whole line has 10 rolling mills in total, the front 3 middle rolling mills and the rear 7 finish rolling mills, the form of the middle finish rolling whole line is vertical-flat, an AGC full-automatic thickness gauge is equipped, the thickness tolerance is controlled, and the start rolling temperature of the middle finish rolling is 990 ℃; and controlling the finish rolling temperature by controlling the finish rolling speed, wherein the finish rolling temperature is 870 ℃, the finish rolling speed is 6m/s, and then the plate chain is subjected to torsion and snake-shaped oscillation to be conveyed and cooled.
(7) Cooling and coiling: and (3) air cooling the rolled steel strip, checking the surface quality and dimensional tolerance, coiling, packaging and warehousing, wherein the coiling temperature is 680 ℃.
Example 2
A preparation method of a 62Si2MnA spring steel hot-rolled steel strip sequentially comprises the following working procedures of electric furnace smelting, LF refining, VD vacuum treatment, continuous casting, heating, descaling, rolling, cooling and coiling, and specifically comprises the following steps:
(1) electric furnace smelting: 40 tons of scrap steel and 70 tons of molten iron are added into an electric furnace, 4000kg of lime and 600kg of dolomite are added in the process of smelting molten steel, and the oxygen supply amount is controlled to be 5000m3Adding 280kg of deoxidizing furnace protecting agent at the smelting end point, staying for 1min, tapping at an eccentric furnace bottom, and controlling the content of C in molten steel to be 0.1 during tapping0%, P content 0.010%, oxygen content 300 ppm; at the end of the smelting process, the initial composition of the molten steel reaches 90% of the lower limit of the target composition.
(2) LF refining: adding 2000Kg of low-aluminum low-titanium ferrosilicon alloy into an LF refining furnace for molten steel alloying, adding 150Kg of high-purity graphite in a small amount and multiple batches for diffusion deoxidation, adding 750Kg of lime and 150Kg of fluorite for slagging, controlling the refining time to be 40min, keeping the white slag for 30min, and controlling the Al2O3 content in the slag to be 5%; the molten steel comprises the following target components in percentage by weight: c: 0.64%, Si: 1.70%, Mn: 0.70%, P0.015%, S0.005%, Cr: 0.24%, Ni: 0.03%, Cu: 0.06 percent, and the balance of iron and trace elements.
(3) VD vacuum treatment: and after the molten steel components of LF refining are qualified, VD vacuum degassing is carried out, the vacuum degree is 1mbar, the processing time is 20min, the covering agent is increased after vacuum breaking, argon is blown softly for stirring for 30min, and the slag surface is slightly moved and does not see light when the stirring is static.
(4) Continuous casting: after the molten steel is subjected to VD vacuum treatment, the ladle is hung to a billet continuous casting machine for casting, a four-flow special tundish with a continuous casting nozzle aperture of phi 38mm and a Y-shaped retaining wall is adopted for casting, the superheat degree is 35 ℃, the casting speed is 1.30m/min, and the constant casting speed is adopted for casting to prepare a small rectangular billet with the size of 150mm multiplied by 220 mm. Wherein the specific water amount is 0.60L/kg, the electromagnetic stirring frequency of the crystallizer is 3.50Hz, and the current is 350A; the electromagnetic stirring frequency at the tail end is 8Hz, and the current is 300A; the center segregation, the center shrinkage cavity and the center porosity of the casting blank are all lower than 1.0 level. The molten steel of the tundish has long retention time, the retention time of each flow of molten steel is close, the components and the temperature are uniform, the dead zone volume is small, and nonmetallic inclusions can be fully collided, grown and floated to be removed.
(5) Heating: the small rectangular billet with the diameter of 150mm multiplied by 220mm is put into a three-section continuous steel pushing type heating furnace and heated in reducing atmosphere, and the residual oxygen content of the flue gas is 3 percent. The heating temperature of the heating furnace is controlled at 1160 ℃, the temperature of the soaking section is controlled at 1120 ℃, and the temperature difference of the section of the billet is less than 30 ℃.
(6) Rolling: and descaling the heated small rectangular billet with the diameter of 150mm multiplied by 220mm by high-pressure water, and then sending the billet into rolling procedures including rough rolling, medium finish rolling and final rolling. Wherein the rough rolling adopts a reciprocating phi 650 and phi 500 rough rolling unit for multi-pass rolling, the initial rolling temperature is 1110 ℃, and the rough rolling is carried out for 6 passes and then the intermediate rolling is carried out; the total middle finish rolling line comprises 10 rolling mills, the first 3 middle rolling mills and the last 7 finish rolling mills, wherein the form of the finish rolling mill is vertical-flat, an AGC full-automatic thickness gauge is arranged, the thickness tolerance is controlled, and the start rolling temperature of the middle finish rolling is 950 ℃; and controlling the finish rolling temperature by controlling the finish rolling speed, wherein the finish rolling temperature is 800 ℃, the finish rolling speed is 7.5m/s, and then carrying out torsion and snake-shaped oscillation to support the plate chain for transportation and cooling.
(7) Cooling and coiling: and (3) air cooling the rolled steel strip, checking the surface quality and dimensional tolerance, coiling, packaging and warehousing, wherein the coiling temperature is 600 ℃.
Example 3
A preparation method of a 62Si2MnA spring steel hot-rolled steel strip sequentially comprises the following working procedures of electric furnace smelting, LF refining, VD vacuum treatment, continuous casting, heating, descaling, rolling, cooling and coiling, and specifically comprises the following steps:
(1) electric furnace smelting: 40 tons of scrap steel and 70 tons of molten iron are added into an electric furnace, 4000kg of lime and 600kg of dolomite are added in the process of smelting molten steel, and the oxygen supply amount is controlled to be 5000m3Adding 300kg of deoxidation furnace protection agent at the smelting end point, staying for 1min, tapping at an eccentric furnace bottom, and controlling the content of C in molten steel to be 0.20%, the content of P to be 0.008% and the content of oxygen to be 230ppm during tapping; at the end of the smelting process, the initial composition of the molten steel reaches 70% of the lower limit of the target composition.
(2) LF refining: adding 2000Kg of low-aluminum low-titanium silicon-iron alloy into an LF refining furnace for molten steel alloying, adding 150Kg of high-purity graphite in a small amount and multiple batches for diffusion deoxidation, adding 750Kg of lime and 150Kg of fluorite for slagging, controlling the refining time to be 70min, keeping the white slag for 50min, and controlling Al in the slag2O3The content is 6 percent; the molten steel comprises the following target components in percentage by weight: c: 0.60%, Si: 1.90%, Mn: 0.85%, P0.010%, S0.003%, Cr: 0.15%, Ni: 0.02%, Cu: 0.05 percent, and the balance of iron and trace elements.
(3) VD vacuum treatment: and after the molten steel components of LF refining are qualified, VD vacuum degassing is carried out, the vacuum degree is 1mbar, the processing time is 10min, the covering agent is increased after vacuum breaking, argon is blown softly and the stirring is carried out for 50min, and the slag surface is slightly moved and does not see light when the stirring is static.
(4) Continuous casting: after the molten steel is subjected to VD vacuum treatment, the ladle is hung to a billet continuous casting machine for casting, a four-flow special tundish with a continuous casting nozzle aperture of phi 38mm and a Y-shaped retaining wall is adopted for casting, the superheat degree is 30 ℃, the casting speed is 1.40m/min, and the constant casting speed is adopted for casting to prepare a small rectangular billet with the size of 150mm multiplied by 220 mm. Wherein the specific water amount is 0.60L/kg, the electromagnetic stirring frequency of the crystallizer is 3.50Hz, and the current is 350A; the electromagnetic stirring frequency at the tail end is 8Hz, and the current is 300A; the center segregation, the center shrinkage cavity and the center porosity of the casting blank are all lower than 1.0 level. The molten steel of the tundish has long retention time, the retention time of each flow of molten steel is close, the components and the temperature are uniform, the dead zone volume is small, and nonmetallic inclusions can be fully collided, grown and floated to be removed.
(5) Heating: the small rectangular billet with the diameter of 150mm multiplied by 220mm is put into a three-section continuous steel pushing type heating furnace and is heated in a reducing atmosphere, and the residual oxygen content of the flue gas is 2.5 percent. The heating temperature of the heating furnace is controlled at 1060 ℃, the temperature of the soaking section is controlled at 1060 ℃, and the temperature difference of the section of the billet is less than 30 ℃.
(6) Rolling: and descaling the heated small rectangular billet with the diameter of 150mm multiplied by 220mm by high-pressure water, and then sending the billet into rolling procedures including rough rolling, medium finish rolling and final rolling. Wherein the rough rolling adopts a reciprocating phi 650 and phi 500 rough rolling unit for multi-pass rolling, the initial rolling temperature is 1030 ℃, and the rough rolling is carried out for 6 passes and then the intermediate rolling is carried out; the middle finish rolling whole line has 10 rolling mills in total, the first 3 middle rolling mills and the last 7 finish rolling mills, the form of the middle finish rolling whole line is vertical-flat, an AGC full-automatic thickness gauge is equipped, the thickness tolerance is controlled, and the middle finish rolling initial rolling temperature is 1030 ℃; and controlling the finish rolling temperature by controlling the finish rolling speed, wherein the finish rolling temperature is 850 ℃, the finish rolling speed is 7.5m/s, and then the plate chain is conveyed and cooled by twisting and snake-shaped oscillation.
(7) Cooling and coiling: and (3) air-cooling the rolled steel strip, checking the surface quality and dimensional tolerance, coiling, packaging and warehousing, wherein the coiling temperature is 650 ℃.
The composition characteristics of the hot rolled steel strip for spring steel produced in examples 1 to 3 of the present invention are shown in Table 1. The thickness of the hot rolled steel strip of the spring steel prepared in examples 1 to 3, the total thickness of the decarburized layer on one side, the type grade of inclusions, and the mechanical properties after quenching and tempering of the cold rolled steel strip finished product were measured, and the results are shown in table 2.
TABLE 1 weight percentages of the components of hot rolled strip of spring steel produced in examples 1 to 3
| C | Si | Mn | P | S | Cr | Ni | Cu | |
| Example 1 | 0.62 | 1.81 | 0.75 | 0.007 | 0.002 | 0.19 | 0.02 | 0.04 |
| Example 2 | 0.64 | 1.70 | 0.70 | 0.015 | 0.005 | 0.24 | 0.03 | 0.06 |
| Example 3 | 0.60 | 1.90 | 0.85 | 0.010 | 0.003 | 0.15 | 0.02 | 0.05 |
TABLE 2 comprehensive properties of hot rolled strip of spring steel produced in examples 1 to 3
TABLE 3 industry control Standard for type and grade of inclusions
| Type of inclusion | Group A sulfides | Class B oxides | Class C silicates | Spherical oxide of class D |
| Thin line | ≤2.0 | ≤2.0 | ≤1.5 | ≤1.5 |
| Coarse series | ≤1.5 | ≤1.5 | ≤1.0 | ≤1.0 |
As can be seen from Table 1, the finished hot rolled steel strip of spring steel prepared by the invention has small fluctuation of chemical components.
The industry control standard of the thickness of the decarburized layer is that when the thickness of the steel strip is less than or equal to 3.00mm, the total decarburized layer on the single surface is less than or equal to 0.08 mm; when the thickness of the steel strip is more than 3.00mm, the total decarburized layer on the single surface is less than or equal to 2.5 percent of the actual thickness. As can be seen from Table 2, when the thickness of the steel strip prepared by the invention is less than or equal to 3.00mm, the total decarburized layers on the single surfaces are 0.04mm and 0.06 mm; when the thickness of the steel strip is more than 3.00mm, the total decarburized layer on the single surface is 0.05mm, so that the decarburized layer on the surface of the finished product of the spring steel hot rolled steel strip prepared by the invention is less and is superior to the existing industry control standard.
The types of the inclusions are divided into A-type sulfides, B-type oxides, C-type silicates, D-type spherical oxides and DS-type large-particle inclusions, wherein the A-type, B-type, C-type and D-type inclusions are divided into fine-system inclusions and coarse-system inclusions, the lower the grade of the inclusions is, the higher the purity of the steel is, and the specific industry control standard is shown in Table 3. As can be seen from the inspection results in Table 2, the inclusions of the steel strip prepared by the invention are only 0.5 grade in the fine system and the coarse system of the D-type spherical oxides, and the balance is 0 grade, which indicates that the finished product of the hot rolled steel strip of the spring steel prepared by the invention has low inclusion content and stable performance of materials in different batches. Meanwhile, the Rockwell hardness of the prepared steel strip cold-rolled finished product after quenching and tempering treatment is 53-54 HRC, 180-degree bending detection is carried out, the toughness is good, the fatigue life of the processed finished product volute spiral spring is long, and the steel strip cold-rolled finished product can be widely applied to the field of automobile safety belts.
Claims (8)
1. A preparation method of a spring steel hot rolled steel strip for a safety belt is characterized by comprising the following steps: the method comprises the working procedures of electric furnace smelting, LF refining, VD vacuum treatment, continuous casting, heating, rolling, cooling and coiling, and specifically comprises the following steps:
(1) electric furnace smelting: smelting molten steel by using an electric furnace, adding lime and dolomite into the furnace, controlling oxygen supply, adding a deoxidation furnace protecting agent at the smelting end point, and tapping at an eccentric furnace bottom, wherein the content of C in the molten steel is controlled to be more than or equal to 0.10 percent, the content of P is controlled to be less than or equal to 0.010 percent, and the content of oxygen in the molten steel is controlled to be less than or equal to 300 ppm;
(2) LF refining: adding alloy into the furnace to carry out molten steel alloying, adding a carburant to carry out diffusion deoxidation, adding lime to carry out slagging, carrying out refining for 40-70 min, keeping white slag for 30-50 min, and controlling Al in the slag2O3The content is less than or equal to 6 percent;
(3) VD vacuum treatment: the vacuum degree is less than or equal to 1mbar, the processing time is more than 10min, and argon is stirred for more than 30min after vacuum breaking;
(4) continuous casting: casting by adopting a four-flow tundish, wherein the superheat degree is 15-35 ℃, and the drawing speed is 1.30-1.40 m/min, so as to prepare a small rectangular blank;
(5) heating: heating the small rectangular blank by adopting a three-section continuous steel pushing type heating furnace, wherein the temperature of a heating section is 1060-1160 ℃, the temperature of a soaking section is 1060-1120 ℃, and the temperature difference of the section of the small rectangular blank is less than 30 ℃;
(6) rolling: descaling the heated small rectangular billet by high-pressure water and then rolling, wherein the rolling comprises rough rolling, medium finish rolling and final rolling; the rough rolling adopts reciprocating multi-pass rolling, and the initial rolling temperature is 1030-1110 ℃; the initial rolling temperature of the medium precision rolling is 950-1030 ℃, and the thickness tolerance is controlled; the finishing temperature is 800-870 ℃;
(7) cooling and coiling: and air-cooling and coiling the rolled steel strip, wherein the coiling temperature is less than or equal to 680 ℃.
2. The method for producing a hot-rolled steel strip for spring steel according to claim 1, characterized in that: and (3) when the smelting process in the step (1) is finished, the initial components of the molten steel reach 70-90% of the lower limit of the target components.
3. The method for producing a hot-rolled steel strip for spring steel according to claim 1, characterized in that: and (3) fine adjustment is carried out on LF refining according to the target components of the molten steel in the step (2).
4. The method for producing a hot-rolled steel strip for spring steel according to claim 2 or 3, characterized in that: the molten steel comprises the following target components: c: 0.60 to 0.64%, Si: 1.70-1.90%, Mn: 0.70-0.85%, P: less than or equal to 0.015%, S: less than or equal to 0.005 percent, Cr: 0.15 to 0.24%, Ni: less than or equal to 0.10 percent, Cu: less than or equal to 0.12 percent, and the balance of iron and trace elements.
5. The method for producing a hot-rolled steel strip for spring steel according to claim 1, characterized in that: the alloy added in the step (2) is low-aluminum low-titanium ferrosilicon alloy and silicon-manganese alloy.
6. The method for producing a hot-rolled steel strip for spring steel according to claim 1, characterized in that: the carburant added in the step (2) is graphite.
7. The method for producing a hot-rolled steel strip for spring steel according to claim 1, characterized in that: in the step (5), the heating atmosphere is a reducing atmosphere, and the residual oxygen content of the flue gas is controlled to be less than or equal to 3 percent.
8. The method for producing a hot-rolled steel strip for spring steel according to claim 1, characterized in that: and (4) in the step (6), the thickness tolerance of finish rolling is less than 0.05 mm.
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| CN115074627A (en) * | 2022-06-28 | 2022-09-20 | 南京钢铁股份有限公司 | Spring steel belt for tape measure and preparation method thereof |
| CN115074604A (en) * | 2022-08-11 | 2022-09-20 | 江苏省沙钢钢铁研究院有限公司 | Spring steel wire rod and production method thereof |
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